Unit pixels, depth sensors and three-dimensional image sensors including the same

ABSTRACT

A unit pixel of a depth sensor includes a light-receiver configured to perform photoelectric conversion of an incident light to output an electrical signal and at least two sensors adjacent to the light-receiver to receive the electrical signal from the light-receiver such that a line connecting the sensors forms an angle greater than zero degrees with respect to a first line, the first line passing through a center of the light-receiver in a horizontal direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Korean PatentApplication No. 10-2011-0043178, filed on May 6, 2011 in the KoreanIntellectual Property Office (KIPO), the entire contents of which areincorporated herein by reference.

BACKGROUND

1. Technical Field

Example embodiments relate generally to semiconductor devices, and moreparticularly to a unit pixel, a depth sensor and a three-dimensionalimage sensor including the unit pixel.

2.Description of the Related Art

Various sensors are widely used for sensing physical quantities such aslight intensity, temperature, mass, time, etc. The sensors may include apixel or a pixel array configured to output electrical signalscorresponding to the physical quantity. Recently, sensors and associatedmethods are developed to measure a distance to an object in addition toa color image of the object.

SUMMARY

Some example embodiments provide a unit pixel and a depth sensor of atime-of-flight (TOF) type including the unit pixel, which may reduce asensing error in measuring a distance to an object.

Some example embodiments provide a depth sensor and a device ofmeasuring a distance and an image such as a three-dimensional imagesensor device, which may enhance a demodulation contrast (DC).

According to example embodiments, a unit pixel of a depth sensorincludes a light-receiver and at least two sensors. The light-receiverperforms photoelectric conversion of an incident light to output anelectrical signal. The sensors are adjacent to the light-receiver toreceive the electrical signal from the light-receiver such that a firstimaginary line connecting the sensors forms an angle greater than zerodegrees with respect to a second imaginary line, where the secondimaginary line passes through a center of the light-receiver in ahorizontal direction.

The light-receiver may be between the sensors and the sensors may beasymmetrical with respect to the second imaginary line and a thirdimaginary line, where the third imaginary line passes through the centerof the light-receiver in a vertical direction perpendicular to thehorizontal direction.

The first imaginary line connecting the sensors may form an anglebetween zero degrees and forty-five degrees with respect to the secondimaginary line.

In some example embodiments, the unit pixel may further include one ormore photo gates on the light-receiver, the photo gates configured tocontrol a transfer of the electrical signal to the sensors depending onvoltages received by the photo gates.

The sensors may correspond one-to-one with the photo gates. At least oneof the sensors may be configured to drain the electrical signal.

In some example embodiments, the unit pixel may further include one ormore transfer gates configured to control a transfer of the electricalsignal to the sensors depending on voltages received by the transfergates, each transfer gate on a region between each sensor and thelight-receiver.

The incident light may include an infrared light.

According to example embodiments, a depth sensor includes a pixel arrayincluding a plurality of unit pixels, and a circuit configured tocalculate distance information based on signals from the pixel array.Each unit pixel includes a light-receiver configured to performphotoelectric conversion of an incident light to output an electricalsignal, and at least two sensors adjacent to the light-receiver toreceive the electrical signal from the light-receiver such that a firstimaginary line connecting the sensors forms an angle greater than zerodegrees with respect to a second imaginary line, the second imaginaryline passing through a center of the light-receiver in a horizontaldirection.

The light-receiver may be between the sensors and the sensors may beasymmetrical with respect to the second imaginary line and a thirdimaginary line, the third imaginary line passing through the center ofthe light-receiver in a vertical direction perpendicular to thehorizontal direction.

The first imaginary line connecting the sensors may form an anglebetween zero degrees and forty-five degrees with respect to the secondimaginary line.

Each unit pixel may further include one or more photo gates on thelight-receiver, the photo gates configured to control a transfer of theelectrical signal to the sensors depending on voltages received by thephoto gates.

In some example embodiments, the depth sensor may further include atiming controller configured to control a timing of applying thevoltages to the photo gates, and a light source configured to output alight signal, the timing controller configured to control the lightsource.

The light signal may include an infrared light and the light source mayinclude a laser diode.

The sensors may correspond one-to-one with the photo gates. At least oneof the sensors may be configured to drain the electrical signal.

Each unit pixel may further include one or more transfer gatesconfigured to control a transfer of the electrical signal to the sensorsdepending on voltages received by the transfer gates, each transfer gateon a region between each sensor and the light-receiver.

According to some example embodiments, a three-dimensional image sensordevice includes a pixel array including a plurality of unit pixels, anda circuit configured to calculate distance information and imageinformation based on signals from the pixel array. Each unit pixelincludes a light-receiver configured to perform photoelectric conversionof an incident light to output an electrical signal, and at least twosensors adjacent to the light-receiver to receive the electrical signalfrom the light-receiver such that a first imaginary line connecting thesensors are asymmetrical with respect to a second imaginary line and athird imaginary line and the first imaginary line connecting the sensorsforms an angle between zero degrees and forty-five degrees with respectto the second imaginary line, the second imaginary line passing througha center of the light-receiver in a horizontal direction, the thirdimaginary line passing through the center of the light-receiver in avertical direction perpendicular to the horizontal direction .

Each unit pixel may further include one or more photo gates on thelight-receiver, and the photo gates may be configured to control atransfer of the electrical signal to the sensors depending on voltagesreceived by the photo gates. The three-dimensional image sensor mayfurther include a timing controller configured to control a light sourceand a timing of applying the voltages to the photo gates, that lightsource configured to output a light signal under a control of the timingcontroller.

The unit pixels may include first pixels configured to sense a distanceto an object and second pixels configured to sense an image of theobject, and the first pixels and the second pixels may be disposedrepeatedly.

At least another example embodiment discloses an image sensor includingat least one pixel including a receiver configured to receive light andconvert the light into an electrical signal, the receiver havingvertical and horizontal axes and at least first and second sensorsadjacent to the receiver, the first and second sensors beingasymmetrical with respect to the vertical and horizontal axes.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative, non-limiting example embodiments will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

FIG. 1 is a top view of a unit pixel of a depth sensor according toexample embodiments.

FIG. 2A is a cross-sectional view of the unit pixel of FIG. 1 takenalong line b-b′.

FIG. 2B is a cross-sectional view of the unit pixel of FIG. 1 takenalong line a-a′.

FIG. 2C is a cross-sectional view of the unit pixel of FIG. 1 takenalong line c-c′.

FIG. 3 is a diagram for describing an effect due to asymmetry of theunit pixel of FIG. 1.

FIG. 4 is a diagram illustrating three-dimensionally iso-potentialsurfaces in FIG. 3.

FIG. 5 is a conceptual diagram of a unit pixel of a depth sensoraccording to example embodiments.

FIG. 6 is a diagram illustrating a distance measurement system accordingto example embodiments.

FIG. 7A is a timing diagram illustrating timings of outputting a lightfrom the light source in FIG. 6 and controlling the photo gates in FIG.5.

FIG. 7B is a diagram illustrating an operation of a depth sensor oftime-of-flight type.

FIG. 8 is a top view of a unit pixel of a depth sensor according toexample embodiments.

FIG. 9 is a cross-sectional view of the unit pixel of FIG. 8 taken alongline e-e′.

FIG. 10 is a cross-sectional view of a unit pixel of a depth sensoraccording to example embodiments.

FIG. 11 is a top view of a unit pixel of a depth sensor according toexample embodiments.

FIG. 12 is a cross-sectional view of the unit pixel of FIG. 11 takenalong line f-f′ or line g-g′.

FIG. 13 is a timing diagram illustrating an operation of a depth sensoradopting a pixel structure according to example embodiments.

FIG. 14 is a diagram illustrating a depth sensor module according toexample embodiments.

FIGS. 15 and 16 are diagrams illustrating systems of measuring an imageand a distance according to example embodiments.

FIG. 17 is a diagram illustrating example layouts of a pixel arrayincluded in the three-dimensional image sensor in FIG. 16.

FIGS. 18 through 23 are circuit diagrams illustrating a unit pixel of adepth sensor according to example embodiments.

FIG. 24 is a block diagram illustrating a camera including athree-dimensional image sensor according to example embodiments.

FIG. 25 is a block diagram illustrating a computing system including athree-dimensional image sensor according to example embodiments.

FIG. 26 is a block diagram illustrating an example of an interface usedin a computing system of FIG. 25.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Various example embodiments will be described more fully hereinafterwith reference to the accompanying drawings, in which some exampleembodiments are shown. Inventive concepts may, however, be embodied inmany different forms and should not be construed as limited to theexample embodiments set forth herein. Rather, these example embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of inventive concepts to those skilled inthe art. In the drawings, the sizes and relative sizes of layers andregions may be exaggerated for clarity. Like numerals refer to likeelements throughout.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are used to distinguish oneelement from another. Thus, a first element discussed below could betermed a second element without departing from the teachings ofinventive concepts. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of inventiveconcepts. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which inventive concepts belong. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 1 is a top view of a unit pixel of a depth sensor according toexample embodiments.

Referring to FIG. 1, a unit pixel 10 of a depth sensor includes alight-receiving region 11 (e.g. a photodiode), isolation regions 14 andtwo sensing regions 13 a and 13 b. The light-receiving region 11 mayalso be referred to as a light-receiver. The two sensing regions 13 aand 13 b may also be referred to as sensors. The light-receiving region11 performs photoelectric conversion of an incident light to output anelectrical signal, and the two sensing regions 13 a and 13 b aredisposed adjacent to the light-receiving region 11 to receive theelectrical signal from the light-receiving region 11. The unit pixel 10may further include two photo gates 12 a and 12 b disposed on thelight-receiving region 11.

Though not illustrated in FIG. 1, the unit pixel 10 may further includea transfer unit and/or an amplification unit to transfer and amplify theelectrical signal from the sensing regions 13 a and 13 b. For example,when the depth sensor is manufactured by complementary metal oxidesemiconductor (CMOS) process, the unit pixel 10 may further include asource follower transistor to amplify the electrical signal from thesensing regions 13 a and 13 b, a circuit to reset the sensing regions 13a and 13 b, and a circuit to select the unit pixel among a plurality ofunit pixels.

The light-receiving region 11 performs photoelectric conversion of anincident light to output an electrical signal. The sensing regions 13 aand 13 b are disposed adjacent to the light-receiving region 11 toreceive the electrical signal from the light-receiving region 11. A lineconnecting the sensing regions 13 a and 13 b forms an angle θ greaterthan zero degree with respect to a first virtual line HL, where thefirst virtual line HL passes through a center of the light-receivingregion 11 in a horizontal direction X. If sensing regions are disposedsymmetrically, the angle between the line connecting the sensing regionsand the first virtual line HL will be zero degree. In contrast, thesensing regions 13 a and 13 b in FIG. 1 are asymmetrical with respect tothe first virtual line HL and a second virtual line VL, where the secondvirtual line VL passes through the center of the light-receiving region11 in a vertical direction Y perpendicular to the horizontal directionX. The line connecting the sensing regions may form the angle θ betweenzero degree and forty-five degrees with respect to the first virtualline HL. Through such asymmetric disposition of the sensing regions 13 aand 13 b, the interval between the sensing regions 13 a and 13 b may beincreased in comparison with the symmetric case. When the two sensingregions 13 a and 13 b operate complementarily, the effect of thedisabled sensing region on the enabled sensing region may be reduced byincreasing the interval between the sensing regions 13 a and 13 b. Inother words, the reduction of the lateral field between the one sensingregion 13 a and the light-receiving region 11 due to the other sensingregion 13 b may be decreased, thereby enhancing the transfer efficiencyof photo charge.

The two sensing regions 13 a and 13 b may operate complementarily andone of the sensing regions 13 a and 13 b may be configured to drain thephoto charge. The draining of the photo charge may reduce the chargesaturation in the sensing region and thus may contribute to realizing awide dynamic range (WDR) of the depth sensor.

When the distance along the horizontal direction X is d from the centerof the light-receiving region 11, the length of the line connection thesensing regions 13 a and 13 b is 2D=2d/cosθ, which is greater than 2 dof the symmetric case. The asymmetry of the sensing regions 13 a and 13b may be varied depending on the angle θ.

The two separate photo gates 12 a and 12 b are illustrated in FIG. 1 asan example, and the one photo gate and three or more photo gates may bedisposed in other embodiments. The photo gates 12 a and 12 b control atransfer of the electrical signal to the sensing regions 13 a and 13 bdepending on voltages applied to the photo gates 12 a and 12 b.

FIG. 2A is a cross-sectional view of the unit pixel of FIG. 1 takenalong line b-b′.

Referring to FIG. 2A, the light-receiving region 11 may be formed in ap-type substrate P-SUB. The light-receiving region 11 may be formed byimplanting p-type impurities, which have the same conduction type as thesubstrate. The light-receiving region 11 may include multiple layers ofn-type impurities and p-type impurities. The photo gates 12 a and 12 bare formed on the light-receiving region 11. The n-type sensing region13 a is disposed to the left of the light-receiving region 11 and theisolation region 14 is disposed to the right of the light-receivingregion 11.

The material of the photo gates 12 a and 12 b may be changed accordingto the light penetrating through the photo gates 12 a and 12 b. Forexample, a transparent and conductive material such as ITO may be usedto transmit the visible light in case of the image pixel for providingthe image information and the opaque material such as polysilicon may beused to transmit the infrared light in case of the depth pixel forproviding the distance information.

Photo charge is generated in the light-receiving region 11 by theincident light. The size and shape of the space charge region, in whichthe generated photo charge is collected, may be varied according to thestructure of the light-receiving region 11. The electrical potential isillustrated at the bottom portion of FIG. 2A, which represents the casewhen the positive voltage is applied to the left photo gate 12 a. Whenthe positive voltage is applied to the photo gate 12 a, the positiveholes are repelled to the substrate P-SUB and the negative electrons arecollected near the upper surface of the light-receiving region 11 underthe photo gate 12 a. The potential gradation, that is, the lateral fieldis caused due to the difference of the impurity density and the appliedvoltage, and thus the photo electrons e move to the sensing region 13 aand the accumulated charge Q1 corresponds to the electrical signal.

FIG. 2B is a cross-sectional view of the unit pixel of FIG. 1 takenalong line a-a′.

Referring to FIG. 2B, the light-receiving region 11 may be formed in thep-type substrate P-SUB, and the photo gates 12 a and 12 b are formed onthe light-receiving region 11. The n-type sensing region 13 b isdisposed to the right of the light-receiving region 11 and the isolationregion 14 is disposed to the left of the light-receiving region 11.

The electrical potential is illustrated at the bottom portion of FIG.2B, which represents the case when the positive voltage is applied tothe right photo gate 12 b. When the positive voltage is applied to thephoto gate 12 b, the positive holes are repelled to the substrate P-SUBand the negative electrons are collected near the upper surface of thelight-receiving region 11 under the photo gate 12 b. The potentialgradation, that is, the lateral field is caused due to the difference ofthe impurity density and the applied voltage, and thus the photoelectrons e move to the sensing region 13 b and the accumulated chargeQ2 corresponds to the electrical signal.

FIG. 2C is a cross-sectional view of the unit pixel of FIG. 1 takenalong line c-c′.

Referring to FIG. 2C, both of the sensing regions 13 a and 13 b may beshown by cutting the unit pixel 10 along the line connecting the sensingregions 13 a and 13 b. The electrical potentials of the two cases areillustrated at the bottom portion of FIG. 2C. The solid line representsthe case when the positive voltage is applied to the left photo gate 12a and the dashed line represents the case when the positive voltage isapplied to the right photo gate 12 b. As mentioned above, the charges Q1and Q2 may be accumulated respectively in the sensing regions 13 a and13 b by controlling the voltages applied to the photo gates 12 a and 12b. The interval 2D between the asymmetric sensing regions 13 a and 13 bmay be increased by 1/cos θ compared with 2 d of symmetric case asunderstood with reference to FIGS. 1, 2A, 2B and 2C.

FIG. 3 is a diagram for describing an effect due to asymmetry of theunit pixel of FIG. 1.

The two circles in FIG. 3 represent the iso-potential surfaces when thepositive voltage is applied to the left photo gate 12 a. The capabilityof each sensing region of attracting the electrons is proportion to avolume within each iso-potential surface. Thus the effect of the staticfield of the disabled sensing region 13 b on the lateral field to theenabled sensing region 13 a may be reduced by increasing the intervalbetween the sensing regions 13 a and 13 b.

FIG. 4 is a diagram illustrating three-dimensionally the iso-potentialsurfaces in FIG. 3.

The iso-potential distribution is shown in FIG. 4 when the unit pixel isseen through the substrate 40 from the bottom. As mentioned above, theeffect of the static field of the disabled sensing region 13 b on thelateral field to the enabled sensing region 13 a may be reduced byincreasing the interval between the sensing regions 13 a and 13 b, thatis, by disposing the sensing regions 13 a and 13 b asymmetrically. As aresult, a demodulation contrast (DC), which is typically used asrepresenting the performance of the time-of-flight (TOF) depth sensor,may be enhanced.

FIG. 5 is a conceptual diagram of a unit pixel of a depth sensoraccording to example embodiments.

As described with reference to FIGS. 1 and 2C, FIG. 5 illustrates thecross-sectional view of a unit pixel 50 taken along line c-c′ of FIG. 1.Referring to FIG. 5, a light-receiving region 51 is disposed in a p-typesubstrate P-SUB and a two sensing regions 53 a and 53 b are disposed toboth sides of the light-receiving region 51. Two photo gates 52 a and 52b are controlled by respective control signals ΦG1 and ΦG2. The controlsignals ΦG1 and ΦG2 may be complementarily-activated signals to transferthe photo electrons generated in the light-receiving region 51alternatively to the sensing regions 53 a and 53 b. The chargesaccumulated in the respective sensing regions 53 a and 53 b are providedas output signals OUT1 and OUT2 through transfer-amplification circuits54 a and 54 b.

When only one of the sensing regions 53 a and 53 b is used to sense thephoto electrons and the other is used to drain the photo electrons, thecorresponding transfer-amplification circuit may be omitted and thedrain voltage is applied to the draining sensing region. For example,when the left sensing region 53 a is used to sense the photo electrons,the transfer-amplification circuit 54 b coupled to the right sensingregion 53 b may be omitted and the power supply voltage VDD as the drainvoltage may be applied to the right sensing region 53 b.

Also the unit pixel may be formed using an n-type substrate. In thiscase, the negative voltage is applied to sense photo holes instead ofthe photo electrons and the ground voltage VSS may be applied to thedraining sensing region.

FIG. 6 is a diagram illustrating a distance measurement system accordingto example embodiments.

Referring to FIG. 6, the distance measurement system 60 may include alight source 61, a timing controller 62, a depth sensor 50 and anoptical lens 63. The light source 61 may illuminate a light to an object64. The light source 61 may include a light-emitting diode (LED). Thetiming controller 62 controls the operational timings of the lightsource 61 and the depth sensor 50. The light from the light source 61 isreflected by the object 64 and the reflected light is input as theincident light to the depth sensor 50 through the optical lens 63. Thedepth sensor 50 includes the pixels according to example embodiments asdescribed with reference to FIGS. 1 through 5. As mentioned above, thedemodulation contrast of the depth sensor may be enhanced through theasymmetry of the sensing regions. The depth sensor outputs the distanceinformation corresponding to the distance R to the object 64 using theasymmetrical sensing regions. The timing controller 62 may synchronizethe light output timing of the light source 61 and the operationaltiming of the depth sensor 50.

FIG. 7A is a timing diagram illustrating timings of outputting a lightfrom the light source in FIG. 6 and controlling the photo gates in FIG.5, and FIG. 7B is a diagram illustrating an operation of a depth sensorof time-of-flight (TOF) type.

Referring to FIG. 7A, the light output from the light source issynchronized with the light emitting timing signal. The first photo gatecontrol signal ΦG1 has substantially the same frequency as the lightemitting timing signal and the first photo gate control signal ΦG1 issynchronized with the light emitting timing signal. The second photogate signal ΦG2 has a phase difference of 180 degrees with respect tothe first photo gate control signal ΦG1. The output light from the lightsource may have the same waveform as the light emitting timing signal.The signals of square waveform are illustrated in FIG. 7A as an example,and the signals may have other waveforms such as sinusoidal waves inother embodiments.

Referring to FIG. 7B, T indicates the on-time of the photo gate and Δtindicates the time difference between the reflected light from theobject 64 and the output light from the light source 61, that is, thelight emitting timing signal. Q1 and Q2 are photo charges measured usingthe complementary photo gate control signals ΦG1 and ΦG2. The photocharges Q1 and Q2 may be measured sequentially using one sensing region,or may be measured respectively by the two asymmetrical sensing regionsas illustrated in FIG. 1. The time difference Δt may be calculated basedon the measured photo charges Q1 and Q2. For example, the differencebetween the measured charges Q1 and Q2 may be used to obtain the timedifference Δt. Accordingly the distance R to the object 64 may beobtained using the relation Δt=2R/c, where c is the light velocity.

FIG. 8 is a top view of a unit pixel of a depth sensor according toexample embodiments.

Referring to FIG. 8, a unit pixel 80 of a depth sensor includes alight-receiving region 81 (e.g. a photodiode), isolation regions 84 andtwo asymmetrical sensing regions 83 a and 83 b. The light-receivingregion 81 performs photoelectric conversion of an incident light tooutput an electrical signal, and the two sensing regions 83 a and 83 bare disposed adjacent to the light-receiving region 81 to receive theelectrical signal from the light-receiving region 81.

In comparison with the unit pixel 10 of FIG. 1, the photo gates areomitted and transfer gates 82 a and 82 b are further included in theunit pixel 80 of FIG. 8. As will be described with reference to FIG. 10,the photo gates may be added to the unit pixel 80 of FIG. 8. Though notillustrated in FIG. 8, the unit pixel 80 may further include a transferunit and/or an amplification unit to transfer and amplify the electricalsignal from the sensing regions 83 a and 83 b.

The sensing regions 83 a and 83 b are disposed adjacent to thelight-receiving region 81 to receive the electrical signal from thelight-receiving region 81. A line connecting the sensing regions 83 aand 83 b forms an angle θ greater than zero degree with respect to afirst virtual line HL, where the first virtual line HL passes through acenter of the light-receiving region 81 in a horizontal direction X. Ifsensing regions are disposed symmetrically, the angle between the lineconnecting the sensing regions and the first virtual line HL will bezero degree. In contrast, the sensing regions 83 a and 83 b in FIG. 8are asymmetrical with respect to the first virtual line HL and a secondvirtual line VL, where the second virtual line VL passes through thecenter of the light-receiving region 81 in a vertical direction Yperpendicular to the horizontal direction X. The line connecting thesensing regions may form the angle θ between zero degree and forty-fivedegrees with respect to the first virtual line HL. Through suchasymmetric disposition of the sensing regions 83 a and 83 b, theinterval between the sensing regions 83 a and 83 b may be increased incomparison with the symmetric case. When the two sensing regions 83 aand 83 b operate complementarily, the effect of the disabled sensingregion on the enabled sensing region may be reduced by increasing theinterval between the sensing regions 83 a and 83 b. In other words, thereduction of the lateral field between the one sensing region 83 a andthe light-receiving region 81 due to the other sensing region 83 b maybe decreased, thereby enhancing the transfer efficiency of photo charge.

The two sensing regions 83 a and 83 b may operate complementarily andone of the sensing regions 83 a and 83 b may be configured to drain thephoto charge. When the distance along the horizontal direction X is dfrom the center of the light-receiving region 81, the length of the lineconnection the sensing regions 83 a and 83 b is 2D=2d/cosθ, which isgreater than 2 d of the symmetric case. The asymmetry of the sensingregions 83 a and 83 b may be varied depending on the angle θ.

FIG. 9 is a cross-sectional view of the unit pixel of FIG. 8 taken alongline e-e′.

Referring to FIG. 9, both of the sensing regions 83 a and 83 b may beshown by cutting the unit pixel 80 along the line connecting the sensingregions 83 a and 83 b. The light-receiving region 81 may include ann-type well (n) and a pinning layer (p+) on the n-type well. Theelectrical potentials of the two cases are illustrated at the bottomportion of FIG. 8. The solid line represents the case when the positivevoltage is applied to the left photo gate 82 a and the dashed linerepresents the case when the positive voltage is applied to the rightphoto gate 82 b. As mentioned above, the charges Q1 and Q2 may beaccumulated respectively in the sensing regions 83 a and 83 b bycontrolling the voltages applied to the photo gates 82 a and 82 b.

FIG. 10 is a cross-sectional view of a unit pixel of a depth sensoraccording to example embodiments.

Referring to FIG. 10, the light-receiving region 101 is disposed in ap-type substrate P-SUB. The photo gates 102 a and 102 b are disposed onthe light-receiving region 101, and the transfer gates 104 a and 104 bare disposed on regions between the light-receiving region 101 and thesensing regions 103 a and 103 b.

In comparison with the unit pixel 80 of FIG. 9, the two photo gates 102a and 102 b are further included in the unit pixel 100 of FIG. 10. Thephoto charges collected under the photo gates 102 a and 102 b aretransferred respectively to the sensing regions 103 a and 103 b throughthe channels 105 a and 105 b formed depending on the on-off operationsof the transfer gates 104 a and 104 b. As mentioned above, through theasymmetric disposition of the sensing regions 103 a and 103 b, theinterval between the sensing regions 103 a and 103 b may be increased incomparison with the symmetric case. Interference between the sensingregions 103 a and 103 b may be reduced and thus the transfer efficiencyof photo charge and the demodulation contrast may be enhanced.

FIG. 11 is a top view of a unit pixel of a depth sensor according toexample embodiments.

Referring to FIG. 11, a unit pixel 110 of a depth sensor includes alight-receiving region 111, isolation regions 114 and two asymmetricsensing regions 113 b and 13 d near the left and right sides of thelight-receiving region 111, two asymmetric sensing regions 113 a and 113c near the upper and bottom sides of the light-receiving region 111 andfour photo gates 112 a, 112 b, 112 c and 112 d disposed on thelight-receiving region 111.

A line connecting the two sensing regions 113 b and 113 d forms anglesθb and θd greater than zero degree with respect to the first virtualline HL, If the sensing regions 113 b and 113 d are disposedsymmetrically, the angles between the line connecting the sensingregions 113 b and 113 d and the first virtual line HL will be zerodegree. The line connecting the sensing regions 113 b and 113 d may formthe angles θb and θd between zero degree and forty-five degrees withrespect to the first virtual line HL.

A line connecting the two sensing regions 113 a and 113 c forms anglesθa and θc greater than zero degree with respect to the second virtualline VL, If sensing regions 113 a and 113 c are disposed symmetrically,the angles between the line connecting the sensing regions 113 a and 113c and the second virtual line VL will be zero degree. The lineconnecting the sensing regions 113 a and 113 c may form the angles θaand θc between zero degree and forty-five degrees with respect to thesecond virtual line VL.

The sensing regions 113 a, 113 b, 113 c and 113 d are disposedasymmetrically with respect to the first virtual line HL and the secondvirtual line VL. Through such asymmetric disposition of the sensingregions, the interval between the sensing regions 113 a and 113 c andthe interval between the sensing regions 113 b and 113 d may beincreased in comparison with the symmetric case. When the sensingregions 113 a through 113 d operate complementarily, the effect of thedisabled sensing region on the enabled sensing region may be reduced byincreasing the interval between the sensing regions. In other words, thereduction of the lateral field between the one sensing region and thelight-receiving region due to the other sensing region may be decreased,thereby enhancing the transfer efficiency of photo charge.

The sensing regions 113 a through 113 d may be enabled sequentiallyusing control signals having a predetermined phase difference, and atleast one of the sensing regions 113 a through 113 d may be configuredto drain the photo charge. The draining of the photo charge may reducethe charge saturation in the sensing region and thus may contribute torealizing a wide dynamic range (WDR) of the depth sensor.

The four separate photo gates 112 a through 112 d are illustrated inFIG. 11 as an example, and the different number of photo gates may bedisposed in other embodiments. The photo gates 112 a through 112 dcontrol a transfer of the electrical signal to the sensing regions 113 athrough 113 d depending on voltages applied to the photo gates 112 athrough 112 d.

FIG. 12 is a cross-sectional view of the unit pixel of FIG. 11 takenalong line f-f′ or line g-g′.

Referring to FIG. 12, both of the sensing regions 113 a and 113 c (or113 b and 113 d) may be shown by cutting the unit pixel 110 along theline connecting the sensing regions 113 a and 113 c (or 113 b and 113d). As mentioned above, the charge transfer to the sensing regions 113 aand 113 c (or 113 b and 113 d) may be controlled by controlling thevoltages applied to the photo gates 112 a and 112 c (or 112 b and 112d).

FIG. 13 is a timing diagram illustrating an operation of a depth sensoradopting an asymmetric pixel structure according to example embodiments.The unit pixel 110 illustrated in FIGS. 11 and 12 may be controlledusing control signals illustrated in FIG. 13.

Referring to FIG. 13, the light output from the light source issynchronized with the light emitting timing signal. The first photo gatecontrol signal ΦG1 has substantially the same frequency as the lightemitting timing signal and the first photo gate control signal ΦG1 issynchronized with the light emitting timing signal. The second photogate signal ΦG2 has a phase difference of 90 degrees with respect to thefirst photo gate control signal ΦG1. The third photo gate signal ΦG3 hasa phase difference of 90 degrees with respect to the second photo gatecontrol signal ΦG2, and the fourth photo gate signal ΦG3 has a phasedifference of 90 degrees with respect to the third photo gate controlsignal ΦG3. The output light from the light source may have the samewaveform as the light emitting timing signal.

FIG. 14 is a diagram illustrating a depth sensor module according toexample embodiments.

Referring to FIG. 14, a depth sensor module 140 may include a depthsensor 141, a timing controller 142, a light source 143 and a lens 144.The light from the light source 143 is reflected by the object 145 andthe reflected light is input as the incident light to the depth sensor141 through the lens 144. The depth sensor 141 may have the enhancedemodulation contrast using the asymmetric sensing regions in the pixelas described above. The depth sensor 141 converts the optical signals tothe electrical signals. The timing controller 142 controls theoperational timings of the depth sensor 141 and the light source 143.For example, the timing controller 142 may synchronize the photo gatecontrol signals to the depth sensor 141 with the output light from thelight source 143.

The light source 143 may include a light source driver 143_1 and a lightgenerator 143_2. The light source driver 143_1 controls the outputtiming of the light generator 143_2 in response to the light emittingtiming signal from the timing controller 142. The light generator 143_2may include, for example, a laser diode for generating an infraredlight.

The depth sensor 141 may include a row decoder XDEC 141_1, a pixel array141_2, an analog-to-digital converter (ADC) 141_3, a memory 141_4 and adepth calculator 141_5.

The pixel array 141_2 may have a plurality of unit pixels as describedwith reference to FIGS. 1 through 13. The ADC 141_3 converts the analogsignals from the pixel array 141_2 to the digital signals. The memory141_4 may be a buffer memory or a frame memory to store the digitalsignals from the ADC 141_3 by the frame unit. The depth calculator 141_5calculates the distance to the object 145 using the data stored in thememory 141_4. The row decoder 141_1 selects one row of the pixel array141_2 and controls the operational timing of the selected row based onthe address signal X-ADD from the timing controller 142.

The depth sensor 141 may be a charge coupled device (CCD) type or a CMOSimage sensor (CIS) type. The structure illustrated in FIG. 14 is similarto the CIS type, and the connection of the ADC 141_3 may be varied incase of the CCD type.

According to correlated double sampling (CDS) scheme, the ADC 141_3 mayhave various structures for analog CDS, digital CDS or dual CDS. TheADC_3 may be a column ADC type that each ADC is coupled to each columnline or a single ADC type that one common ADC is used for all columnlines.

In some embodiments, the depth sensor 141 and the timing controller 142may be integrated in a single chip. In other embodiments, the depthsensor 141, the timing controller 142 and the lens 144 may be formedinto one module and the light source 143 may be formed into anothermodule.

FIGS. 15 and 16 are diagrams illustrating systems of measuring an imageand a distance according to example embodiments.

Referring to FIG. 15, a system 150 may include a timing controller 151,a light source 152, a depth sensor 153 for measuring the distanceinformation and an image sensor 154 for measuring the image information.The sensors 153 and 154 may be coupled to respective lenses 155 and 156.The timing controller 151 controls the operational timings of the lightsource 152 and the sensors 153 and 154.

The depth sensor 153 receives through the lens 155 the incident light,which is output from the light source 152 and reflected by the object157, and outputs the distance information Dout. The image sensor 154receives through the lens 156 the optical signals representing thecaptured image of the object 157 and outputs the image information Cout.The depth sensor 153 and the image sensor 154 may be implemented as therespective chips. The depth sensor 153 includes at least one unit pixelincluding the asymmetric sensing regions as described with reference toFIGS. 1 through 13.

Referring to FIG. 16, a system 160 may include a timing controller 161,a light source 162 and a three-dimensional image sensor 163 formeasuring the distance information in addition to the image information.The lens 164 is coupled to the three-dimensional image sensor 163. Thetiming controller 161 controls the operational timings of the lightsource 152 and the three-dimensional image sensor 163.

The three-dimensional image sensor 163 may include a pixel array inwhich image pixels and depth pixels are arranged in a predeterminedpattern. The three-dimensional image sensor 163 outputs the distanceinformation Dout using the depth pixels based on the reflected lightfrom the object 165. In addition, the three-dimensional image sensor 163outputs the image information Cout using the image pixels based on theoptical signals representing the captured image of the object 165. Thedepth pixel includes the asymmetric sensing regions as described withreference to FIGS. 1 through 13.

FIG. 17 is a diagram illustrating example layouts of a pixel arrayincluded in the three-dimensional image sensor in FIG. 16.

FIG. 17 shows various example patterns (a) through (e) of the pixelarray including the depth pixels Z and the image pixels R, G and B, andalso other patterns may be adopted to form the pixel array of thethree-dimensional image sensor 163 of FIG. 16. The red pixel R, thegreen pixel G and the blue pixel B are used as the image pixels in FIG.17 as an example, and alternatively pixels such as a magenta pixel, acyan pixel, a yellow pixel and a white pixel may be used as the imagepixels.

Referring to FIG. 17 (a), a unit pattern of 2*2 matrix may include onedepth pixel Z and three color pixels R, G and B, and the pixel array mayinclude a plurality of the unit patterns repeated in the row directionand the column direction.

Referring to FIG. 17 (b), a unit pattern of 3*2 matrix may include twodepth pixels Z and Z and the four color pixels R, G, G and B.

Referring to FIG. 17 (c), a pixel array may include image pixels R, Gand B arranged in the Bayer pattern and depth pixels four times largerthan each image pixel.

Referring to FIG. 17 (d), a pixel array may include an upper layer inwhich the color pixels R, G and B are arranged in the Bayer pattern anda bottom layer in which the depth pixels Z four times larger than eachimage pixel are arranged.

Referring to FIG. 17 (e), a pixel array may include four stacked layersin which the three color pixels R, G and B and the depth pixels arearranged, respectively. The layers for the respective pixels may bedetermined depending on the penetration depths of the correspondinglight. For example, the blue pixels B corresponding to the visible lightof the shortest wavelength may be formed in the uppermost layer, and thedepth pixel Z corresponding to the infrared light of the longestwavelength may be formed in the lowest layer.

FIGS. 18 through 23 are circuit diagrams illustrating a unit pixel of adepth sensor according to example embodiments.

Two paired pixels are illustrated in FIG. 18. The pixels include photogates PG1 and PG2 responding to gate control signals Pa and Pb, transfertransistors TX1 and TX2 responding to transfer control signals TG1 andTG2, sensing regions FD1 and FD2, reset transistors RX1 and RX2responding to a reset signal RS, drive transistors DX1 and DX2, andselection transistors SX1 and SX2 responding to a selection signal SEL,respectively.

In some example embodiments, each pixel may include its ownlight-receiving region (not shown). In this case, each pixel may includetwo asymmetric sensing regions as described with reference to FIGS. 1through 13, but only one sensing region per pixel is illustrated in FIG.18 for convenience of description. The illustrated sensing region FD1 orFD2 is used for sensing and not-illustrated sensing region may be usedfor draining to realize wide dynamic range (WDR).

In other example embodiments, the two pixels in FIG. 18 may share onelight-receiving region (not shown). In this case, the photo gates PG1and PG2 are separated to operate complementarily and the two sensingregions FD1 and FD2 may be disposed asymmetrically near thelight-receiving region.

Referring to FIG. 19, the two pixels may share the light-receivingregion (not shown), the sensing region FD, the reset transistor RX1, thedrive transistor DX1 and the selection transistor SX1. As mentionedabove, the not-illustrated sensing region for draining may be disposedasymmetrically the sensing region FD near the light-receiving region.

FIG. 20 illustrates an example similar to that of FIG. 18 but thetransfer transistors TX1 and TX2 are omitted. FIG. 21 illustrates anexample similar to that of FIG. 19 but the transfer transistors TX1 andTX2 are omitted.

Referring to FIG. 22, the unit pixel may include a light-receivingregion (not shown), a photo gate PG on the light-receiving region, atransfer transistor Tx, a sensing region FD, a reset transistor RX, adrive transistor Dx and a selection transistor SX. Even though onesensing region FD is illustrated in FIG. 22, the unit pixel may includeanother sensing region (not shown) for draining, which is disposed nearthe light-receiving region asymmetrically with the illustrated sensingregion FD. FIG. 23 illustrates an example similar to that of FIG. 22 butthe transfer transistor TX is omitted.

FIG. 24 is a block diagram illustrating a camera including athree-dimensional image sensor according to example embodiments.

Referring to FIG. 24, a camera 240 includes a lens 241, athree-dimensional image sensor 242, a motor unit 243 and an engine unit244. The three-dimensional image sensor 242 may include the image sensorand the depth sensor as illustrated in FIG. 15 or one integrated sensorchip as illustrated in FIG. 16. The three-dimensional image sensor 242includes at least one unit pixel of asymmetric sensing regions asdescribed with reference to FIGS. 1 through 13. A light source may beincluded in the three-dimensional image sensor 242.

The lens 241 may focus the incident light on the light-receiving regionof the depth pixels and/or the color pixels of the three-dimensionalimage sensor 242. The three-dimensional image sensor 242 may generatedata DAT including the distance information and/or the color imageinformation based on the incident light passing through the lens 241.The three-dimensional image sensor 242 may provide the data DAT to theengine unit 244 in response to a clock signal CLK. In exampleembodiments, the three-dimensional image sensor 242 may interface withthe engine unit 244 using a mobile industry processor interface (MIPI)and/or a camera serial interface (CSI).

The motor unit 243 may control the focusing of the lens 241 or mayperform shuttering in response to a control signal CTRL received fromthe engine unit 244. The engine unit 244 may control thethree-dimensional image sensor 242 and the motor unit 243. The engineunit 244 may process the data DAT received from the three-dimensionalimage sensor 242. For example, the engine unit 244 may generatethree-dimensional color data based on the received data DATA. In exampleembodiments, the engine unit 244 may generate YUV data including aluminance component, a difference between the luminance component and ablue component, and a difference between the luminance component and ared component based on the data DAT, or may generate compressed data,such as joint photography experts group (JPEG) data. The engine unit 244may be coupled to a host/application 245, and may provide the dataYUV/JPEG to the host/application 245 based on a master clock signalMCLK. In example embodiments, the engine unit 244 may interface with thehost/application 245 using a serial peripheral interface (SPI) and/or aninter integrated circuit (12C) interface.

FIG. 25 is a block diagram illustrating a computing system including athree-dimensional image sensor according to example embodiments.

Referring to FIG. 25, a computing system 250 includes a processor 251, amemory device 252, a storage device 253, an input/output device 254, apower supply 255 and a sensor 256.

The sensor 256 may include the image sensor and the depth sensor asillustrated in FIG. 15 or one integrated sensor chip as illustrated inFIG. 16. The sensor 256 includes at least one unit pixel of asymmetricsensing regions as described with reference to FIGS. 1 through 13. Alight source may be included in the sensor 256.

Although it is not illustrated in FIG. 25, the computing system 250 mayfurther include a port for communicating with electronic devices, suchas a video card, a sound card, a memory card, a USB device, etc.

The processor 251 may perform specific calculations and/or tasks. Forexample, the processor 251 may be a microprocessor, a central processunit (CPU), a digital signal processor, or the like. The processor 251may communicate with the memory device 252, the storage device 253 andthe input/output device 254 via an address bus, a control bus and/or adata bus.

The processor 251 may be coupled to an extension bus, such as aperipheral component interconnect (PCI) bus. The memory device 252 maystore data for operating the computing system 250. For example, thememory device 252 may be implemented by a dynamic random access memory(DRAM), a mobile DRAM, a static random access memory (SRAM), a phasechange random access memory (PRAM), a resistance random access memory(RRAM), a nano floating gate memory (NFGM), a polymer random accessmemory (PoRAM), a magnetic random access memory (MRAM), a ferroelectricrandom access memory (FRAM), or the like. The storage device 253 mayinclude a solid state drive, a hard disk drive, a CD-ROM, or the like.The input/output device 254 may include an input device, such as akeyboard, a mouse, a keypad, etc., and an output device, such as aprinter, a display device, or the like. The power supply 255 may supplypower to the computing device 250.

The sensor 256 may be coupled to the processor 251 via the buses orother desired communication links. The sensor 256 and the processor 251may be integrated in one chip, or may be implemented as separate chips.The computing system 250 may be any computing system including thesensor 256 according to example embodiments. For example, the computingsystem 250 may include a digital camera, a mobile phone, a smart phone,a personal digital assistant (PDA), a portable multimedia player (PMP),or the like.

FIG. 26 is a block diagram illustrating an example of an interface usedin a computing system of FIG. 25.

Referring to FIG. 26, a computing system 260 may employ or support aMIPI interface, and may include an application processor 2600, athree-dimensional image sensor 2620 and a display device 2630. A cameraserial interface (CSI) host 2602 of the application processor 2600 mayperform a serial communication with a CSI device 2621 of thethree-dimensional image sensor 2620 using a CSI. In example embodiments,the CSI host 2602 may include a deserializer DES, and the CSI device2621 may include a serializer SER.

The three-dimensional image sensor 2620 may include the image sensor andthe depth sensor as illustrated in FIG. 15 or one integrated sensor chipas illustrated in FIG. 16. The three-dimensional image sensor 2620includes at least one unit pixel of asymmetric sensing regions asdescribed with reference to FIGS. 1 through 13. A light source may beincluded in the three-dimensional image sensor 2620.

A display serial interface (DSI) host 2601 of the application processor2600 may perform a serial communication with a DSI device 2631 of thedisplay device 2630 using a

DSI. In example embodiments, the DSI host 2601 may include a serializerSER, and the DSI device 2631 may include a deserializer DES.

The computing system 260 may further include a radio frequency (RF) chip2640. A physical layer PHY 2603 of the application processor 2600 mayperform data transfer with a physical layer PHY 2641 of the RF chip 2640using a MIPI DigRF. The PHY 2603 of the application processor 2600 mayinterface (or, alternatively communicate) a DigRF MASTER 2604 forcontrolling the data transfer with the PHY 2641 of the RF chip 2640. Thecomputing system 260 may further include a global positioning system(GPS) 2610, a storage device 2650, a microphone 2660, a DRAM 2670 and/ora speaker 2680. The computing system 260 may communicate with externaldevices using an ultra wideband (UWB) communication 2693, a wirelesslocal area network (WLAN) communication 2692, a worldwideinteroperability for microwave access (WIMAX) communication 2691, or thelike. However, example embodiments are not limited to configurations orinterfaces of the computing systems 250 and 260 illustrated in FIGS. 25and 26.

Example embodiments may be used in any three-dimensional image sensor orany system including the three-dimensional image sensor, such as acomputer, a digital camera, a three-dimensional camera, a mobile phone,a personal digital assistant (PDA), a scanner, a navigator, a videophone, a monitoring system, an auto focus system, a tracking system, amotion capture system, an image stabilizing system, or the like.

The foregoing is illustrative of example embodiments and is not to beconstrued as limiting thereof. Although a few example embodiments havebeen described, those skilled in the art will readily appreciate thatmany modifications are possible in the example embodiments withoutmaterially departing from the novel teachings and advantages ofinventive concepts. Accordingly, all such modifications are intended tobe included within the scope of inventive concepts as defined in theclaims. Therefore, it is to be understood that the foregoing isillustrative of various example embodiments and is not to be construedas limited to the specific example embodiments disclosed, and thatmodifications to the disclosed example embodiments, as well as otherexample embodiments, are intended to be included within the scope of theappended claims.

1. A unit pixel of a depth sensor, the unit pixel comprising: alight-receiver configured to perform photoelectric conversion of anincident light to output an electrical signal; and at least two sensorsadjacent to the light-receiver to receive the electrical signal from thelight-receiver such that a first imaginary line connecting the sensorsforms an angle greater than zero degrees with respect to a secondimaginary line, the second imaginary line passing through a center ofthe light-receiver in a horizontal direction.
 2. The unit pixel of claim1, wherein the light-receiver is between the sensors and the sensors areasymmetrical with respect to the second imaginary line and a thirdimaginary line, the third imaginary line passing through the center ofthe light-receiver in a vertical direction perpendicular to thehorizontal direction.
 3. The unit pixel of claim of claim 1, wherein thefirst imaginary line connecting the sensors forms an angle between zerodegree and forty-five degrees with respect to the second imaginary line.4. The unit pixel of claim 1, further comprising: one or more photogates on the light-receiver, the photo gates configured to control atransfer of the electrical signal to the sensors depending on voltagesreceived by photo gates.
 5. The unit pixel of claim 4, wherein thesensors correspond one-to-one with the photo gates.
 6. The unit pixel ofclaim 1, wherein at least one of the sensors is configured to drain theelectrical signal.
 7. The unit pixel of claim 1, further comprising: oneor more transfer gates configured to control a transfer of theelectrical signal to the sensors depending on voltages received by thetransfer gates, each transfer gate on a region between each sensor andthe light-receiver.
 8. The unit pixel of claim 1, wherein the incidentlight includes an infrared light.
 9. A depth sensor comprising: a pixelarray including a plurality of unit pixels; and a circuit configured tocalculate distance information based on signals from the pixel array,wherein each unit pixel includes, a light-receiver configured to performphotoelectric conversion of an incident light to output an electricalsignal; and at least two sensors adjacent to the light-receiver toreceive the electrical signal from the light-receiver such that a firstimaginary line connecting the sensors forms an angle greater than zerodegrees with respect to a second imaginary line, the second imaginaryline passing through a center of the light-receiver in a horizontaldirection.
 10. The depth sensor of claim 9, wherein the light-receiveris between the sensors and the sensors are asymmetrical with respect tothe second imaginary line and a third imaginary line, the thirdimaginary line passing through the center of the light-receiver in avertical direction perpendicular to the horizontal direction.
 11. Thedepth sensor of claim 9, wherein the first imaginary line connecting thesensors forms an angle between zero degree and forty-five degrees withrespect to the second imaginary line.
 12. The depth sensor of claim 9,wherein each unit pixel further includes one or more photo gates on thelight-receiver, the photo gates configured to control a transfer of theelectrical signal to the sensors depending on voltages received by thephoto gates.
 13. The depth sensor of claim 12, further comprising: atiming controller configured to control a timing of applying thevoltages to the photo gates; and a light source configured to output alight signal, the timing controller configured to control the lightsource.
 14. The depth sensor of claim 13, wherein the light signalincludes an infrared light and the light source includes a laser diode.15. The depth sensor of claim 12, wherein the sensors correspondone-to-one with the photo gates. 16-20. (canceled)
 21. An image sensorcomprising: at least one pixel including, a receiver configured toreceive light and convert the light into an electrical signal, thereceiver having vertical and horizontal axes, and at least first andsecond sensors adjacent to the receiver, the first and second sensorsbeing asymmetrical with respect to the vertical and horizontal axes. 22.The image sensor of claim 21, wherein the first and second sensors areat a same angle with respect to the horizontal axis and a midpoint ofthe receiver.
 23. The image sensor of claim 21, wherein the first sensoris configured to operate based on a first control signal and the secondsensor is configured to operate based on a second control signal, thefirst and second control signals being complimentary.
 24. The imagesensor of claim 21, wherein the first sensor is configured to operatebased on a first control signal and the second sensor is configured toreceive a power supply voltage.
 25. The image sensor of claim 21,wherein the receiver includes p-type impurities and the first and secondsensors include n-type impurities.